Many surgical procedures require that surgical instruments such as retractor blades be positioned in a number of different positions in order to perform a certain surgical task. It is desirable that the operating surgeon or surgical assistant be able to directly move the retractor blade into various positions and configurations that may be required. It is also desirable that any surgical retractor that may be used to achieve such positions and configurations not obstruct the surgical site, and be able to avoid any obstacles that may exist around the surgical site, such as medical imaging systems, operating room lights, instrument trays, or other apparatus. The surgical retractor should also be stable, easy to control and re-position precisely, require no attention between changes in position in order to free the surgeon's hands to perform other tasks, and be sufficiently strong and rigid to hold a set position reliably, yet be light enough to allow the surgeon to easily achieve a desired position and orientation of the retractor blade. It is also desirable that the surgical retractor sense pressures in the retracted tissue near a location under the retractor blade, alert the surgeon of any potentially hazardous pressures, and automatically regulate retraction pressures and positions, thereby reducing the likelihood of tissue laceration and ischemia caused by the retractor blade during long procedures.
Various methods for positioning and holding retractor blades are known in the prior art. One common method for positioning a retractor blade is to have a surgical assistant hold the retractor blade in a desired position, and change the position when and as requested by the operating surgeon. This task is fatiguing for the surgical assistant, and may not provide sufficiently precise and rigid support for the retractor blade in some surgical procedures.
In addition to the method for positioning described above, apparatus for positioning retractor blades exists in the art. One typical retractor blade positioning apparatus consists of a vertical mounting frame fastened to the operating room table, to which are fastened at discrete but adjustable positions different retractor blades to provide an upward pulling force on tissues or organs (e.g. Aesculap BT710 Fixation Device and Aesculap BT711-BT715 Rochard abdominal retractor blades, Aescualp Instruments Corp, Burlingame, Ca. U.S.A.). Ropes, weights, and pulley systems are also used in conjunction with the vertical frame to provide a continuously adjustable positioning system. Similar abdominal retraction techniques utilize a horizontal frame laid on the patient's body to which are fastened at discrete but adjustable positions different retractor blades to provide a lateral pulling force on tissues or organs (e.g. Aesculap BV662 frame and Aesculap BV668 blades). These types of surgical retractors are difficult to set up and take down, clumsy to adjust, and often obstruct the surgical site. Furthermore, adjusting such apparatus to achieve a new position may require the assistance of a non-sterile person, in that operating room fixtures and support stands that may require re-positioning are not considered sterile, hence cannot be touched by a surgeon. This may preclude optimal positioning of the retractor blades or tissue, as the surgeon may no longer have direct control over the final position of the retractor blade. These types of retractor blade positioning systems are limited in their range of adjustment, versatility of orientation, precision of positioning, and rigidity of support. They also offer no means to sense and regulate applied retraction pressures.
Additional specialized positioning devices for holding retractor blades are known in the art. The Elmed Company of Addison Illinois manufactures a multi-jointed mechanism, the "Elmed Retract-Robot", catalog number 15088-00 single arm instrument, which can be locked in a wide range of positions with a thumb-screw arrangement. However this device is not suitable for a wide range of surgical procedures due to its inconsistent locking strength, limited range of motion, inability to unlock joints separately for re-positioning, time-consuming and tedious adjustment of the thumb screw, potential for obstruction of the surgical site, and solid steel construction which is not x-ray translucent. It is conceivable that several such devices could be connected together to create a larger structure with an increased range of motion, but such a structure would be very difficult to re-position, in that each device in the structure would have to be unlocked, positioned and locked individually each time a new position is required. In addition, it is unlikely that several such devices connected together would offer sufficient strength for the intended application. Finally, this device offers no means for sensing or regulating retraction pressures.
Also known in the art is a retractor blade holding device, widely known by surgeons throughout the world as a "Greenberg" brain retractor. This surgical retractor consists of a plurality of ball and socket joints, threaded upon a length of cable. This cable may be tightened with a lever mechanism to increase the friction between each ball and socket joint. The Greenberg brain retractor is not suitable for all surgical procedures due to its typically small size. In addition, the strength of the ball and socket joints when fully locked is insufficient to support the loads typically expected when positioning retractor blades in many surgical procedures. The device is not x-ray translucent, nor is it capable of sensing or regulating retraction pressure.
One problem that is common to any re-positionable surgical retractor is achieving sufficient strength and rigidity to provide a stable structure for the intended application, using only materials and mechanisms that are sterilizable, self-contained, and suitably clean for use in surgical procedures. Although many examples of locking mechanisms are known in the prior art, most are either too large, too weak when scaled down to a size appropriate for this application, or use fluid in a force multiplying system which is unsuitable in surgical applications due to concerns about leaks. In addition, the use of fluid as a force multiplying component requires that some means be provided to bleed air or other gasses from the fluid to render it substantially incompressible, which requires complex and specialized apparatus. A better means of achieving force multiplication would use a material which provides the function of a hydraulic amplifier over a very small range of motion, but which does not use fluids.
One example of a locking mechanism suitable for use in a non-sterile surgical environment is disclosed in U.S. Pat. No. 4,807,618, entitled "Patient Limb Positioning Apparatus". This apparatus uses a pneumatic actuator which exerts a high force on a system of levers which in turn exert force on a ball joint mechanism in order to lock it in place. This force multiplying mechanism is not suitable for use in applications where the device must be sterilized, because the materials and mechanisms used will not withstand the sterilization procedures used in hospitals. A further disadvantage of this type of mechanism is that it requires a relatively large number of very high strength components in order to operate properly.